Weed Science (2003) 51, 740-747

Ryouichirou Tsuji, Albert J. Fischer, Masahiro Yoshino, Alvaro Roel, James E. Hill and Yuji Yamasue (2003)
Herbicide-resistant late watergrass (Echinochloa phyllopogon): similarity in morphological and amplified fragment length polymorphism traits
Weed Science 51 (5), 740-747
Abstract: Late watergrass is a serious weed of California rice that has evolved resistance to molinate, thiobencarb, fenoxaprop-ethyl, and bispyribac-sodium. To obtain an insight into the origin and spread of resistant (R) late watergrass in California rice fields, we evaluated similarities in morphological traits and amplified fragment length polymorphism (AFLP) fingerprints among 15 R strains compared with susceptible (S) strains. All strains were derived by inbreeding from accessions collected in rice fields of the Sacramento Valley, CA. In the field, R plants were shorter than S plants; they also had narrower and shorter flag leaves and thinner culms. Spikelets also appeared smaller and more slender in R plants. There was greater morphological similarity among the 15 R strains than among the eight S strains. The mean coefficients of variation for morphological traits were much smaller among R strains, which in a cluster analysis (Ward's method) were grouped morphologically apart at early clustering stages from the more variable S strains. AFLP electropherograms also showed greater similarity between R strains. R strains were grouped separately from the S strains in a cluster analysis based on calculated Nei and Li coefficients used in an unweighted pair group method using arithmetic means. However, small genetic differences also existed because the R strains were grouped into six clusters, suggesting that R strains were not samples from an identical strain. It was concluded that R strains originated from a preexisting and preadapted mutant late watergrass population in the Sacramento Valley. This study establishes that resistance moved by spikelet dispersal, not independent mutation events, most likely defined the geographical distribution of R late watergrass in California. Prevention and control of this dispersal combined with elimination of seed-producing survivors after herbicide treatment should be relevant components of the integrated management of herbicide-resistant late watergrass in California rice.
(The abstract is excluded from the Creative Commons licence and has been copied with permission by the publisher.)
Link to article at publishers website
Database assignments for author(s): Albert J. Fischer, Yuji Yamasue

Research topic(s) for pests/diseases/weeds:
pesticide resistance of pest
population dynamics/ epidemiology

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Pest and/or beneficial records:

Beneficial	Pest/Disease/Weed	Crop/Product	Country	Quarant.
	Echinochloa phyllopogon (weed)	Rice (Oryza)	U.S.A. (SW)